A disconnect switch is a mechanical device used for changing the connections in a circuit or for isolating a circuit or other equipment from a power source. One type of disconnect switch is the double motion, double-sided break switch, an example of which is depicted in FIG. 1. As explained in more detail below, it is conventional in disconnect switches to employ a movable switch blade that is first rotated from a pivot point so as to move into the region of a cooperating jaw contact. During a part of this rotational movement, the blade is rotated about its longitudinal axis so as to bring its beavertail contact(s) into rigid engagement with the cooperating contact surfaces of the jaw(s). This provides good engagement under pressure between the jaw contacts and the beavertail contact(s). See, for example, U.S. Pat. No. 3,388,225, Jun. 11, 1968, titled "Jaw For Ice Breaking Switch."
FIG. 1 depicts a recent example of a prior art disconnect switch 10. In this embodiment, three electrical insulator stacks 12a, 12b, and 14 are mounted on a common base. The two outside stacks 12a, 12b are rigidly mounted and have terminal pads for connection to a circuit. The center stack 14 is mounted on a bearing 16 so that it can rotate about its longitudinal axis by operation of a crank 16a or the like. The two outside stacks 12a, 12b support first and second resilient contact jaw members 18a, 18b. As the center stack 14 rotates, a housing 20 through which a conducting tube or blade 22 passes makes or breaks the circuit as shown in FIGS. 2A and 2B. FIG. 2A depicts the conducting blade 22 in an open position, and FIG. 2B depicts the blade in a closed position.
As the disconnect switch approaches a fully closed position, the blade 22 first enters the stationary contacts 18a, 18b as shown in FIG. 3 and then rotates into a fully closed position as shown in FIG. 4. That is, the blade 22 rotates about the longitudinal axis of the center insulator 14 until the contact portions 24a, 24b enter the contact jaws 18a, 18b respectively, at an inclined angle. At this point, the blade 22 rotates about its longitudinal axis so that the contact portions 24a, 24b rotate to a vertical position as shown in FIG. 4. This latter rotation provides the wiping motion needed to insure good contact and to allow the switch 10 to perform under icing conditions. This arrangement reduces the operating forces needed to close the switch 10. Traditionally, in the prior art, this rotation of the blade 22 has been accomplished as shown schematically in FIG. 5. In the arrangement depicted in FIG. 5, the center stack 14 (FIG. 1) is rotated so that the blade 22 assumes the "partially closed" position, i.e., a position in which the blades ends are in contact with the jaws but at an inclined angle. At this point, the blade hits the stationary contacts 18a, 18b and will not travel any further. However, the center insulator stack 14 continues to rotate, which forces rotation of the blade about the blade's axis 34 by means of a gear arrangement. This is schematically depicted in FIG. 5 as a linkage 30 attached at a connection point 32 to a collar crank that engages the blade 22 and rotates it about the blade's longitudinal axis 34. A force vector 36 is also depicted in FIG. 5. Thus, in this prior art arrangement, the blade rotates about its own axis by means of a force or movement at the end of a crank, lever, or gear.
Of course, there are other features of the prior art that are known to those skilled in the art. For example, both the blade and jaw contacts utilize high-pressure, silver-to-copper construction. Furthermore, throughout the current carrying parts, all bolts, nuts and pins are stainless steel, minimizing the possibility of corrosion. A galvanized structural steel channel base is used to support the insulators and live parts, providing strength and rigidity. The contact blades are preferably heavy, one piece tubular aluminum with replaceable copper contacts at each end. Silver-surfaced edges of the contact ends engage with tinned copper jaw fingers to provide a silver-to-tinned copper contact. The rotating motion of the blade provides a self-cleaning wiping of the contacts. Contact pressure is applied to the copper jaw fingers by stainless steel springs, which are insulated at one end. Jaw contact pressure is increased as current increases due to a reverse loop finger design. Magnetic forces due to fault currents tend to push the blade deeper into the jaw. The number of contact fingers provided is varied depending on the current carrying capability of the switch.